Evaluation of Incomplete Stent Apposition of Flow Diverters at the Aneurysm Neck on Aneurysm Healing and Endothelialization: An OCT- and Histopathology-Based Study

BACKGROUND AND PURPOSE: Incomplete stent apposition (ISA) of flow diverters (FDs) at the aneurysm neck has been associated to delayed occlusion. However, the influence of ISA severity on endothelialization and aneurysm healing remains unclear. This study aimed to quantify ISA severity in porcine aneurysm models, assess its temporal evolution, and determine its impact on occlusion and endothelialization. METHODS: Sidewall aneurysms were surgically created in the left common carotid arteries of 15 Bama mini pigs, followed by FD deployment. Baseline 2D-digital subtraction angiography (2D-DSA) measured aneurysm dome, neck, and parent artery diameters. Optical Coherence Tomography (OCT) measured maximum, minimum, and mean stent-wall distances at the neck plane. DSA and OCT were performed at 4, 8, and 12 weeks to evaluate stent patency and ISA progression. At 12 weeks, all animals were euthanized for histopathological examination. Logistic regression assessed the association between ISA severity and incomplete endothelialization or delayed occlusion. RESULTS: All 15 pigs successfully underwent aneurysm model and FD implantation. Immediate post-procedural OCT identified varying degrees of ISA at the aneurysm neck in all animals (15/15), with mean maximum, minimum, and average distances of 690.74 μm, 415.47 μm, and 554.10 μm, respectively. Excluding one pig that died from vessel occlusion at 4 weeks, DSA showed progressive aneurysm occlusion, with complete occlusion rates of 50% (7/14), 57.1% (8/14), and 64.3% (9/14) at 4, 8, and 12 weeks, respectively. OCT demonstrated a gradual reduction in ISA over time, with 9/14 (64.3%) cases showing complete stent apposition at 12 weeks. Histopathological analysis at 12 weeks was consistent with these findings. Further analysis revealed that stents with maximum ISA distance >600 μm or fluctuation amplitude >50 μm were independently associated with delayed occlusion and poor endothelialization (P = 0.01 for both). CONCLUSION: Severe ISA impairs endothelialization and aneurysm healing. A maximum ISA >600 μm or amplitude >50 μm represent predictive thresholds for adverse outcomes after FD implantation.